Thermal fluid flow indicator



Feb. 27, 1951' D. o. NELSON 2,543,588

mami. FLUID FLow INDICATOR Filed Oc'.. 7, 1946 /3 g2/0 /5 FLUID FLow 0 n FLUID FLow INVENTOR. DONALD O. NELSON .BY my ATTORNEY Patented Feb. 27, 1951 THERMAL FLUID FLOW INDICATOR Donald O. Nelson, West Los Angeles, Calif., as-

signor to Bendix Aviation Corporation. South Bend. Ind., a corporation of Delaware Application Octbel' 7, 1946, Serial No. 701,854

Claims.

This invention relates to devices for indicating whether or not fluid is flowing and has as a broad object to provide a reliable, and compact, device for this purpose.

Another object is to provide a flow indicator with substantial and known las of response so that it will produce an indication only a predetermined interval after flow has begun or stopped.

Another object is to provide a flow indicator that is responsive to the flow integrated over an interval of time, so as to produce an indication either in response to a small change in flow continuing for a substantial interval or a larger change in flow continuinglor a shorter interval.

Another object is to provide a flow indicator in which the only object exposed to the fluid now is a small streamlined, sealed body.

Another object is to provide a flow indicator adapted to produce an indication at a point remote from the point of measurement.

Other more specific objects and features of the invention will become apparent from the description to follow.

The invention in its simplest form comprises a body immersed in the fluid. the state of flow of which is to be indicated, with a source of heat and two temperature responsive elements within the body, one element being closer to the heat source than the other, in combination with means differentially responsive to the two elements.

The operation o! the invention is based upon the fact that when there is little or no fluid flow past the body there is relatively little heat conducted away from the body by the fluid. Therefore the heat generated by the heat source spreads throughout the body by rotation and conduction so that the temperature responsive element that is remote from the heat source is heated to a substantial temperature not much lower than the temperature responsive element that is closer to the heat source. 0n the other hand, when uid flow occurs put the body, heat is removed from the body into the fluid by convection at a relatively rapid rate, thereby producing a much lower temperature in portions of the body remote from the heat source than closely adjacent thereto. This temperature difference is effective upon the two temperature responsive elements to produce a differential force that is employed to actuate an indicating device.

The differentially responsive means may be of various types. In one form of the apparatus the two temperature responsive elements can consist of thermostatic devices having electrical contacts thereon, and so arranged that when the two elements are at different temperatures the contacts are closed but when the two elements are at substantially the same temperature the contacts are open, or vice versa. Another device that can be employed is a thermocouple arranged with one set of junctions closer to the heat source than the other set. During fluid flow the set of junctions adjacent the heat source will be substantially warmer than the junctions more remote from the heat source,y causing the production of a thermal E. M. F. of much greater magnitude than when there is no fluid flow and both sets of Junctions are at very nearly the same temperature.

A full understanding` of the invention may be had from the following detailed description taken in connection with the drawing, in which:

Fig. 1 is a longitudinal sectional view through one embodiment of the apparatus in accordance with the invention; and

Fig. 2 is a similar view showing another embodiment.

Referring first to Fig. 1, there is disclosed a fluid flow pipe I I within which the state of uid motion is to be indicated. The apparatus in accordance with the present invention includes a body I0 which is contained within'the pipe II, a battery 20, a battery 2 I, an alarm bell I8 and conducting wires extending into the body Il.

In the particular construction shown in Fig. 1, the body I0 is of teardrop-shape having formed integrally therewith, a bracket 22 which extends through the wall of the pipe II and is welded thereto as indicated at 23 to form a iiuid tight joint. 'Ihls bracket 22 defines a passage 24 extending from the exterior of the pipe I I into the interiorof the body I0 for the passage of electrical conductors 25 and 2i respectively.

There is positioned within a chamber 21 in the forward part of the body III a helical bi-metallic strip Il which is anchored at one end as by a screw 28 to the wall of the chamber 21 and is anchored at its other end as by a screw 29 to an axial shaft 30 which is journaled at one end in a bearing 3| provided in the forward end wall of the chamber 21. The other or rear end of the shaft 30 extends through and is journaled in a wall 32 which forms a closure for the chamber 21. There is mounted on the shaft 30 rearwardly of the wall 32 a contact arm 33 which carries an electrical contact I5. This contact arm 33 is insulated from the shaft'30 by any suitable means and is connected to the conductor 26.

There is positioned in a chamber 35 formed in the rear portion of the body I0 a second helical bi-metallic strip I6 which is anchored at one end by a screw 36 to the body III and is anchored at its other end by a screw 31 to a shaft 38, which is journaled for rotation similarly to the shaft 30. The shaft 38 is electrically connected to the body I0 and carries a contact arm 40 having a contact I1. The paths of movement of the contacts I5 and I1 coincide so that they come together in response to relative rotation of the two slss-.its 30 and 38 respectively. When the contacts I5 and I1 make, they complete a circuit for energization the bi-metallic helix I4 a heating coil Il which may as shown surround the chamber 21 in which the helix Il is positioned. This heating element I3 is energized from the battery 2li over the conductor 25 and a return circuit including the body Iii and the pipe II.

The arrangement can be such that during iiuid ow through the pipe II the contacts I5 and I1 are open, but when fluid ilow stops the contacts close to give an alarm. To this end the relative length of the bi-metallic helices I4 and I6 is such that when the helix I4 is substantially warmer than the helix I6 the contacts I5 and I1 are separated, but raising of the temperature of the helix IB moves the contact I1 against the contact I5. During fluid Ilow the body In loses heat rapidly by convection to the iiuid moving therepast so that the rear portion of the body III remote from the heating element I3 is strongly cooled. On the other hand the temperature oi.' the helix Il is only slightly ailected by the rate of cooling of the body I because of its close proximity to the heat element I3.

It will be obvious that if it is desired to produce an alarm in response to nuid flow instead of in response to cessation of uid flow, this result can be obtained by suitable initial adjustment of the relative positions of the contacts I and I1, so that they are separated when the helices I4 and IB are both at substantially the same temperature but are moved together in response to a decrease in the temperature o! the helix I6 below that of the helix Il.

In the modified form of the invention shown in Fig. 2, a thermocouple 5D is substituted for the helices I4 and I6 and their associated elements including the contacts I5 and I1. The thermocouple has its hot junctions 5I positioned within the heating element I3a and its cold junctions 52 positioned within the rear end of the body IDa relatively remote from the heating element I3a. As in Fig. 1, the heating element I3a is energized over a conductor 25a from a battery 20a and the thermocouple 50 is connected by leads 60 to a relay 6I having contacts 62.

The operation of the arrangement of Fig. 2 is readily apparent. When the heating element Ila is energized and there is fluid ow through the pipe I Ia, the hot junctions 5I of the thermocouple are at a substantially higher temperature than the cold junctions 52, thereby generating an E. M. F., which causes current to iiow, actuating relay 6I to close its contacts 62. The contacts 62 can be connected in any suitable alarm circuit not shown.

On the other hand, when uid ow through the pipe I Ia ceases, theentire body I0a warms up, thereby elevating the temperature of the cold junctions 52 to a temperature near that o! the hot junctions 5I, causing a decrease in the thermal current and the release of the relay 6I.

Obviously, if desired, the relay 6I can be adapted to close its contacts when released instead of when energized.

Although for the purpose of explaining the invention several specific embodiments thereof have been described in detail, many departures from the exact constructionsshown can be made without departing from the invention which is t0 be limited only to the extent Bet forth in the appended claims.

I claim:

1. Apparatus ot the type described comprising: a closed body member adapted to be supported in a iiuid stream to be tested; a source of heat localized within a portion only of said body member: a pair of temperature-responsive elements in said body member one or said elements being positioned in substantially better heat-transmission relation with respect to said source than the other element, and said other element being positioned in at least as good heat-transmission relation with respect to said body member as said one element, whereby said other element varies in temperature to substantially greater extent than said one element in response to variations in temperature oi' said body member; and means responsive to a predetermined temperature relation between said elements.

2. Apparatus of the type described comprising: a body member adapted to be supported in a iiuid stream to betested: a source of heat localized within a portion only of said body member; a pair oi' temperature-responsive elements in said body member asymmetrically disposed in asymmetric heat transmission relation to said heat source; and means responsive to av predetermined temperature relation between said elements, said body member consisting of a fluid-tight casing containing said source of heat and said temperature-responsive elements whereby transfer oi' heat from said source to said stream takes place solely through said casing.

3. Apparatus according to claim 11 in which said source of heat and one of said temperatureresponsive elements are positioned adjacent the upstream end of said body member relative to said other temperature-responsive element.

4. Apparatus of the'type described comprising: a body member adapted to be supported in a fluid stream to be tested; a source of heat localized within a portion only of said body member; a pair of temperature-responsive elements in said body member, one of which elements is substantially closer to said source of heat than is the other said temperature-responsive element; and means responsive to a predetermined temperature relation between said elements. l

5. Apparatus of the type described comprising: a body member adapted to be supportzd in a iluid stream to be tested; a source of heat localized within a portion only of said body member; a pair of temperature-responsive elements in said body member asymmetrically disposed in asymmetric heat transmission relation to said heat source; and means responsive to a predetermined temperature relation between said elements; said temperature-responsive elements including a pair of coaxial axially-spaced helical bimetallic elements having their remote ends anchored against relative movement, and having on their adjacent ends cooperating contacts movable in a common circular path concentric with respect to the axis of said helices.

DONALD Oi NELSON.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 2,165,569 Obermaier July 11, 1939 2,431,241 Godsey, Jr. Nov. 18, 1947 

